In recent, there have been increasing cases where images of a human body in a horizontal axis direction, a longitudinal axis direction, a diagonal direction and other directions are acquired by using a magnetic resonance imaging (MRI) device, and the state of a person to be examined is examined and diagnosed through the images.
In general, in case of the magnetic resonance imaging device, a main magnetic field is applied to a measurement space, but there is a problem since an intended strength of a magnetic field (e.g., 3 tesla) is not consistently applied.
Since perturbation or variation of the main magnetic field causes artifacts in a reconstructed image, a technology that maps and corrects the main magnetic field is necessary.
The technology that corrects the main magnetic field may be divided largely by the following two (2) manners: a phase based field mapping manner; and a frequency based field mapping manner.
In case of the phase based field mapping manner, since images can be reconstructed through one sequence, there is an advantage in that the main magnetic field can be quickly corrected. However, when the phase exceeds 360° from 0°, a phase wrapping problem occurs, and a separate follow-up process to resolve the problem has been necessary.
In case of the frequency based magnetic field mapping manner, the phase wrapping problem does not occur, but there has been a problem in that since each image of multiple saturation frequencies needs to undergo one sequence, an overly long period of time for imaging is necessary.
Meanwhile, in this regard, WO 2009/042881 A1 (Title of Invention: Frequency Referencing for Chemical Exchange Saturation Transfer MRI) describes a water saturation shift referencing (WASSR) technique performed by using a magnetic resonance scanner. The water saturation shift referencing technique corrects the main magnet field based on frequency shift of a water molecule.